1. Field of the Invention
The present invention relates to a control device of a high-pressure fuel system of an internal combustion engine that includes fuel injection means (in-cylinder injector) for injecting a fuel into a cylinder at a high pressure, or an internal combustion engine that includes, in addition to the above fuel injection means, fuel injection means (intake manifold injector) for injecting a fuel into an intake manifold or an intake port. More particularly, the present invention relates to a technique for controlling a high-pressure fuel system having a plurality of high-pressure fuel pumps.
2. Description of the Background Art
An engine having a first fuel injection valve (in-cylinder injector) for injecting a fuel into a combustion chamber of a gasoline engine and a second fuel injection valve (intake manifold injector) for injecting a fuel into an intake manifold, and changing a fuel injection ratio between the in-cylinder injector and the intake manifold injector in accordance with the engine speed or the load of the internal combustion engine is known. A direct injection engine having only a fuel injection valve (in-cylinder injector) for injecting a fuel into a combustion chamber of a gasoline engine is also known. In a high-pressure fuel system including the in-cylinder injector, the fuel having its pressure increased by a high-pressure fuel pump is supplied via a delivery pipe to the in-cylinder injector, which injects the high-pressure fuel into a combustion chamber of each cylinder of the internal combustion engine.
Further, a diesel engine having a common rail fuel injection system is also known. In the common rail fuel injection system, the fuel having its pressure increased by a high-pressure fuel pump is stored in a common rail, and injected from the common rail into a combustion chamber of each cylinder of the diesel engine according to opening/closing of an electromagnetic valve.
To obtain the fuel of a high pressure in such internal combustion engines, a high-pressure fuel pump is used which has a cylinder driven by a cam provided at a driveshaft that is connected to a crankshaft of the internal combustion engine.
Japanese Patent Laying-Open No. 11-044276 discloses a fuel injection apparatus that reduces fluctuation of fuel pressure in common rails due to discharge pulsation of high-pressure pumps so as to stabilize the amount of the fuel injected. The fuel injection apparatus includes first and second high-pressure pipes having their proximal ends connected to a fuel tank, first and second high-pressure pumps provided at certain positions on the first and second high-pressure pipes, respectively, and driven at timings to cancel the discharge pulsation with each other, first and second common rails formed in tubular bodies provided with injection valves and connected to the tip ends of the first and second high-pressure pipes, respectively, to inject the fuel discharged from the first and second high-pressure pumps into the engine, and a connection pipe arranged between the discharge sides of the first and second high-pressure pumps and the first and second common rails so as to connect the first and second high-pressure pipes.
According to this fuel injection apparatus, the discharge pulsation of the fuel caused by the first and second high-pressure pumps would interfere one another through the connection pipe. At this time, the first and second high-pressure pumps are driven at timings to cancel the discharge pulsation with each other. For example, when the first high-pressure pump is in a discharge stroke, the second high-pressure pump is in an intake stroke. Thus, the peak of discharge pulsation by the first high-pressure pump and the trough of discharge pulsation by the second high-pressure pump can cancel each other. As such, the fuel with reduced pulsation can be supplied from the first and second high-pressure pipes toward the first and second common rails, so that fluctuation in fuel pressure in each of the common rails can be suppressed.
Japanese Patent Laying-Open No. 2001-263144 discloses a fuel pressure control apparatus for an internal combustion engine capable of suppressing excessive increase of an actual fuel pressure exceeding its target value due to erroneous excessive increase of an integral term when the amount of the fuel discharged from a fuel pump is approximate to or equal to its maximum value. This fuel pressure control apparatus for an internal combustion engine has a fuel pump for discharging a fuel into a fuel pipe, and controls in a feedback manner the amount of the fuel discharged from the fuel pump based on an actual fuel pressure within the fuel pipe and its target value such that the actual fuel pressure approaches the target value. The control apparatus includes means for calculating a controlled variable for use in the feedback control of the amount of the fuel discharged from the fuel pump based on the integral term updated in accordance with a difference between the actual fuel pressure and its target value, and means for inhibiting the update of the integral term toward the increase side in which the amount of the fuel discharged from the fuel pump is increased, when the amount of the fuel discharged is approximate to or equal to the maximum value thereof.
When the amount of the fuel discharged from the fuel pump is approximate or equal to the maximum value at the start of the engine or the like, even if the integral term is updated so as to increase the fuel pressure to a target value, the fuel pressure will not increase rapidly. As such, the integral term may erroneously be changed to the side to excessively increase the amount of the fuel discharged. In contrast, according to the above-described configuration of the fuel pressure control apparatus for an internal combustion engine, update of the integral term toward the side causing increase in amount of the fuel discharged is inhibited when the amount of the fuel discharged from the fuel pump is approximate or equal to its maximum value. Accordingly, it is possible to suppress occurrence of so-called overshoot, which is a considerable rise of the actual fuel pressure exceeding the target value, due to the change of the integral term toward the side causing excessive increase of the amount of the fuel discharged, when the amount of the fuel discharged from the fuel pump is approximate or equal to the maximum value.
However, although the fuel injection device disclosed in Japanese Patent Laying-Open No. 11-044276 has two high-pressure fuel pumps connected to each other via a connection pipe, there is no disclosure of detailed control of the high-pressure fuel pumps. The fuel pressure control apparatus for an internal combustion engine disclosed in Japanese Patent Laying-Open No. 2001-263144 does feedback control of only one high-pressure fuel pump.
When two or more high-pressure fuel pumps are connected via a connection pipe to supply a high-pressure fuel into one high-pressure fuel system, the high-pressure fuel pumps are controlled in a feedback manner. At this time, control duties of the high-pressure fuel pumps are changed to control the amounts of the fuel discharged therefrom, so as to attain a desired fuel pressure. In such a case, if the controlled variable (especially, integral term) used for the feedback control is fixed regardless of change in number of operating high-pressure fuel pumps, good controllability of the fuel pressure before and after the switching in number of the operating high-pressure fuel pumps cannot be expected due to the difference between the individual high-pressure fuel pumps.